Question

(20 points) What is true about the forces in circular motion situations?

A. The net force is opposite the motion.

B. The net force is parallel to the motion.

C. The net force is perpendicular to the motion.

D. There are no forces.

I'm pretty sure the answer is B. "parallel to the motion" but I thought I'd double check because this test is open book. Please explain your answer as well :)

Answer 1

C. The net force is perpendicular to the motion.

When you swing a yo-yo in a circle around your head, the net force
is the tension in the string, pointing toward the center of the circle. 
There's nothing there that provides any force parallel or opposite to
the motion.

When the Earth revolves around the Sun in a circular orbit, the net force
is the gravitational force between the Sun and the Earth.  There's nothing 
there that provides any force parallel or opposite to the motion.